The Economist has a good article about the Mormon church. It mentions that the church has grown tremendously since it was first founded in New York by Joseph Smith and now has more members outside the U.S. than inside. There’s also the debate of whether to call it a worldwide church or a U.S. church with foreign adherents.
Rodney Stark, an American sociologist, pronounced 20 years ago that the Mormon faith was on the way to becoming the first world religion to be founded since Muhammad; he thought the number of adherents might exceed 260m by the second half of the 21st century.
Since then, the rate of growth has eased a little, though it remains impressive compared with many Christian denominations.
The article mentions Mitt Romney and Brandon Flowers as prominent Mormons.
It also mentions that church membership in Brazil (where I spent two years as a Mormon missionary) and Mexico constitute 1 million of the Church’s almost 13 million members.